In the late spring of 218 B.C., Hannibal left New Carthage in Spain with the purpose of crossing the French Alps in order to invade Italy and defeat Rome. By the time he reached the passes in the Alps, he had an army of 38,000 infantry, 8,000 cavalry, and 37 war elephants. It was an arduous crossing. By the time he crossed over into Italy, he had only 20,000 infantry, 4,000 cavalry, and only a few of the elephants.
Many of the Gaul tribes, who were residing in the Po Valley were in revolt against Rome. These made easy recruits for Hannibal.
After a minor confrontation with Roman forces under Publius Cornelius Scipio, in which Scipio was defeated, Hannibal was to pick up even more recruits for his army, replacing all of his losses while crossing the Alps (except for the elephants).
Hannibal defeated the Romans in two more engagements; Trebia, and Lake Trasimene.
After this, Rome under Fabius Maximus opted for a strategy of avoiding a major battle with Hannibal, preferring instead to limit his movements and harass his supply. Hannibal, however managed to extricate himself and defeat this strategy and went into winter quarters unmolested.
In the spring of 216 B.C. Hannibal again seized the initiative.
The town of Cannae, on the Aufidus River was a major Roman supply depot just off the western coast of Italy. Hannibal seized the town cutting Rome off from a major source of supply. He made camp just to the east of Cannae and waited for Rome to send an army to meet him.
Rome obliged. The "Fabius Strategy" was discarded, and a combined Roman and Allied army of 86,000 men was sent southeast to deal with Hannibal.
This army was commanded by two consuls -- Lucius Aemilius Paullus and Gaius Terentius Varro. It was the Roman practice at that time when there were multiple consuls to alternate command of the army from day to day.
Hannibal, of course knew this.
Paullus had a reputation for being prudent and cautious. Varro, on the other hand, was less so. He was even considered by some to be reckless.
Hannibal knew this also, and was counting on Varro being in command on the day of the battle.
As the Romans were approaching Cannae in late July, they were ambushed by a small contingent of the Carthaginians and were driven off. Varro was in command that day, and his confidence as well as the rest of the army's was significantly bolstered.
The Romans arrived in the Cannae area and set up camp on July 31st. They actually set up two camps. Their main camp, with two thirds of the army, was on the same side of the river about three miles to the west of Hannibal's camp. A second fortified camp was set up across the river. The purpose of this camp was to protect the foraging parties from the main camp, and to harass those of the enemy.
For two days, the two armies just stayed where they were. On August 1, Hannibal, who was aware that Varro would be in command the next day, crossed the river and offered battle. Paullus refused.
It apparently was just what Hannibal wanted. He sent his cavalry to harass the Romans gathering water outside their fortifications at the smaller Roman camp, disrupting their efforts to resupply their army with water.
On August 2, Varro took the bait and deployed his men.
Standard doctrine at the time was to extend the infantry in line at the center, with cavalry on the flanks. The Romans had 86,000 men to Hannibal's 56,000. What Varro did was to compact and compress his infantry center to add more weight. So instead of his line being longer than Hannibal's by virtue of having more men, the affect of this compacting was to make his line about the same length as Hannibal's.
As the two armies approached each other. Hannibal did the opposite of Varro. His plan was to create a situation where a "double envelopment" of the Roman army was possible.
Hannibal put his best troops, the Carthaginians, on both ends of the infantry line. The center infantry was made up of Gauls and other troops. As the armies neared contact, Hannibal spread out his forces weakening the center and strengthening the flanks. Doing this "on the run" created a crescent shape in his line with the middle of the crescent closest to the advancing Romans.
The Romans were also advancing with the eastern sun in their eyes. The wind was also blowing from the east kicking up dust and making visibility difficult.
And there was no water.
On the flanks, Hannibal's cavalry defeated and scattered the outmatched and outnumbered Roman cavalry.
In the center, the Roman infantry with its added weight pushed back the center of Hannibal's line, now creating a reverse crescent shape. This drew the Romans in.
But Hannibal's Carthaginians on the ends of the infantry line were not yet engaged. They proceeded to curl around the Roman line hitting them in their flanks.
At the same time, the victorious Carthaginian cavalry closed in on the rear of the Roman infantry. The Romans, having nowhere to go jammed into one another to the point of not even being able to use their weapons.
The slaughter now began. As the Romans were cut down on the fringes, the jammed together men in the center were simply cut down where they stood,
It was said that 600 legionaries were slaughtered every minute until darkness put an end to the killing. Only 14,000 Roman and Allied troops managed to escape -- cutting their way out to the nearby town of Canusium. It was one of the worst defeats in the history of the Roman army.
Hannibal is said to have lost around 8,000 men.
The battle is still studied by military historians as being one of the first successful instances of the "double envelopment" and the "pincers movement".
